Sc 2O 3–W matrix impregnated cathode with spherical grains

Abstract

Sc 2O 3–W matrix cathodes have been prepared by using a liquid–liquid doping method combined with high-temperature sintering. The microstructure and physical behavior of active substances of scandia-doped tungsten matrix and impregnated cathode has been studied by SEM and AES methods. The results show that the matrix has a homogeneous structure composed of W grains with spherical shape and superfine Sc 2O 3 particles dispersed uniformly over and among W grains. After impregnation, this Sc-type impregnated cathode has high emission capability. Space-charge-limited current density could reach 52 A/cm 2 at 850 °C b. The high emission results from a Ba–Sc–O active layer with a thickness of about 80 nm, which is formed at the cathode surface during the activation period. Both the decrease of the thickness of active surface layer and the decrease of the content of Sc at the surface could lead to the degradation of current density during operation.